1. Field of the Invention
The present invention relates to a second-refrigerant pump driving type air conditioner, and more particularly, to a second-refrigerant pump driving type air conditioner capable of performing a heating operation, reducing a restriction of a length and a diameter of a connection pipe for connecting an outdoor unit and an indoor unit, and preventing an oil shortage of a compressor.
2. Description of the Background Art
Generally, an air conditioner is provided with an indoor unit for heating or cooling an indoor room, and an outdoor unit for providing a compressed refrigerant to the indoor unit.
As shown in FIG. 1, the air conditioner comprises a plurality of indoor units 10, and a plurality of outdoor units 20 for providing a refrigerant according to a driving state of each indoor unit 10.
Each indoor unit 10 comprises an indoor heat exchanger 11 for heat-exchanging the refrigerant with indoor air, and an indoor side expander 13 disposed at an inlet of the indoor heat exchanger 11 for depressurizing and expanding the refrigerant.
Each outdoor unit 20 comprises a compressor 21, and an outdoor heat exchanger 27 connected to the compressor 21 for heat-exchanging the refrigerant with outdoor air. A common accumulator 23 for sucking a gaseous refrigerant into each compressor 21 is installed at an inlet of the compressor 21, and a four-way valve 25 for switching a refrigerant channel is installed at an outlet of the compressor 21. An outdoor expander 29 is installed at one side of the outdoor heat exchanger 27 along a flow direction of the refrigerant. Also, a bypass 31 having a check valve 33 is formed at one side of the outdoor expander 29. Each outdoor unit 20 is provided with service valves 35, and a connection pipe 37 for distributing or integrating the refrigerant is provided between each outdoor unit 20 and each indoor unit 10.
When the air conditioner is operated, the outdoor units 20 are selectively driven in correspondence with a load amount of the indoor unit 10 being driven among the plural indoor units 10. Each four-way valve 25 of the outdoor unit 20 being driven switches a refrigerant channel according to a driving mode of the indoor unit 10. When the indoor unit 10 is operated in a cooling mode, the four-way valve 25 of the outdoor unit 20 being driven switches a refrigerant channel so that the refrigerant discharged from the compressor 21 can pass through the outdoor heat exchanger 27. The refrigerant that has passed through the outdoor heat exchanger 27 passes through the indoor side expander 13 of the indoor unit 10 being driven, thereby being depressurized and expanded. The depressurized and expanded refrigerant is heat-exchanged with indoor air by the indoor heat exchanger 11, thereby performing a cooling operation. Then, the refrigerant is sucked into the compressor 21 via the four-way valve 25 and the accumulator 23 of the outdoor unit 20, thereby being compressed, discharged, and circulated, repeatedly.
Oil is filled in the compressor 21 with a refrigerant so as to cool and lubricate the compressor 21. Accordingly, oil is dispersed in the indoor unit 10 including the indoor heat exchanger 11 and in the connection pipe for connecting the indoor unit 10 and the outdoor unit 20 to each other.
In the conventional air conditioner, a pressure more than a certain degree has to be maintained in the connection pipe so that the oil remaining in the indoor heat exchanger 11 and the connection pipe can be smoothly recollected into the compressor 21. Therefore, there is a limitation in increasing a diameter of the connection pipe to a value more than a certain value, and a length of the connection pipe has to be maintained as a value less than a certain value. Accordingly, there is a distance limitation between the outdoor unit 20 and the indoor unit 10.
Furthermore, an oil recollecting driving for recollecting oil remaining in the indoor heat exchanger 11 and each connection pipe is periodically performed (for example, 6 to 8 hours). When the oil recollecting driving is performed, noise is generated and a cooling/heating operation is stopped thereby to cause a user's inconvenience.